1. Field of the Invention
The present invention relates to an ink jet recording head for recording by ejecting ink to a recording medium.
2. Description of the Related Art
Recently, a number of recording apparatuses have been used, and high speed, high resolution, high image quality, low noise, etc., are required for these recording apparatuses. Recording apparatuses which meet these requirements include an ink-jet type recording apparatus (hereinafter, referred to as ink jet recording apparatus). An ink jet recording apparatus is configured to eject ink (recording liquid) droplets from recording head ejectors, and to perform recording by letting these ink droplets adhere to a recording medium. In this ink jet recording apparatus, since recording is performed by means of ink ejection from a recording head, recording can be performed without any contact to a recording medium to realize an extremely stable recording image.
FIG. 8 is a perspective view showing a conventional ink jet recording head, a part of which is cut out. The ink jet recording head includes a heater 1, which is an electro-thermal conversion element corresponding to each ejector 4, and a separator wall for forming each independent nozzle 5, which is a flow path of ink, is provided to extend from the ejector 4 to a vicinity of a supply chamber 6. Such a recording head has an ink ejecting device according to an ink jet recording method disclosed in Japanese Patent Laid-Open No. H4-10940, and is configured such that an air bubble generated at an ink ejection is conducted to outside air via an ejector.
Factors for judging a recording quality include a granularity. An outstanding granularity in a recording output reduces a recording quality thereof. Therefore, in order to make granularity unnoticeable, a conventional recording method proposes to provide nozzles ejecting ink droplets with different sizes, and to perform recording using a small ink droplet for a portion with a bright-tone to a half-tone in an image and to perform recording using a large ink droplet for a portion with a half-tone to a dark-tone.
Also, Japanese Patent Laid-Open No. 2004-1491 proposes to arrange nozzles ejecting large and small ink droplets symmetrically in the main scanning direction, in which an ink jet recording head scans, for averaging an effect of air flow to a flying ink droplet by realizing a bi-directional recording to improve an image quality.
FIG. 9 is a diagram showing a nozzle arrangement disclosed in Japanese Patent Laid-Open No. 2004-1491. A nozzle column 15 ejecting a large droplet and a nozzle column 16 ejecting a small droplet are arranged with the same nozzle pitch, respectively, and the large and small nozzles are arranged to be shifted by half a nozzle pitch each other. Further, for a symmetrical arrangement of nozzles, an additional column is arranged for respective large and small nozzles and the large and small nozzle columns are arranged to be shifted by half a nozzle pitch each other. Such a symmetrical configuration of large and small nozzle columns is applied for only cyan and magenta and a configuration with only a large nozzle column is applied for yellow. Although nozzles with the same ejection amount are actually shifted by half a pitch between left and right in FIG. 9, this arrangement is assumed here to be symmetrical for convenience.
In a case such a configuration having large and small nozzles in symmetry is employed, many nozzles are arranged along the main scanning direction of an ink jet recording head (hereinafter, also referred to simply as “recording head”) and the width of the ink jet recording head becomes large. When a recording head with a large width is attached to a recording apparatus being tilted and recording is performed in this situation, a shift of an ink droplet landing position by the tilt becomes significant and appears in a recording result.
FIG. 10 is a schematic plan view showing an arrangement state of two types of nozzles, large and small, ejecting ink with each color arranged along the main scanning direction in a recording head. In FIG. 10, a CL column A, CS column A, CS column B and CL column B, which are allocated near the both ends of the recording head in the main scanning direction, are nozzle columns for ejecting cyan ink. In this case, the distance between the nozzles at the both ends, that is, CL column A and CL column B, is 6 mm.
FIG. 11A is a diagram showing positional relationships of ink droplets at landing for recording by the CL column A, CS column A, CS column B and CL column B, column by column for easy understanding, in a case a recording head is not tilted. FIG. 11B is a diagram showing an appearance of landed ink droplets in a case the recording head is not tilted. FIG. 11C is a diagram showing positional relationships of ink droplets at landing, column by column for easy understanding, in a case a recording is performed with the recording head tilted by approximately 0.2 degree, and FIG. 11D is a diagram showing an appearance of landed ink droplets in a case with the recording head in a tilted state.
When the recording head is not tilted, ejected ink droplets land on a recording medium approximately at positions according to a nozzle arrangement as shown in FIG. 11A and the ink droplets fill a recording area uniformly as shown in FIG. 11B.
On the other hand, when the recording head is tilted, ejected ink droplets land at positions in a state tilted different from arrangement of each nozzle as shown in FIG. 11C. As a result, portions where ink droplets ejected from the CL column A and CL column B overlap each other come to increase and a recording area in a recording medium can not be filled with ink droplets sufficiently, resulting in that a white line will appear in a recoding result as shown in FIG. 11D. This phenomenon is apparent in a case where a diameter of a small nozzle is as small as one third of that of a large nozzle and a nozzle pitch is large, and a recording unevenness with a particular period, caused by a periodical change of a recording head tilt during scanning, further worsens the problem.